System and method for stimulating the heart in combination with cardiac rhythm management pharmaceuticals

ABSTRACT

Sensors are applied to the heart and sensor data is supplied to a rules engine. The rules engine applies rules that reflect a CRM pharmaceutical regime of the patient to the sensor data to determine whether an electrical waveform should be applied to the heart. When electrical stimulation is warranted, the drug “awareness” rules are used by the rules engine to instruct a multi-phase cardiac stimulus generator to generate an electrical waveform that improves the performance of the drugs administered to the patient, allow the patient to be administered a lower dose of a particular drug, and/or reduce or eliminate side effects from the drugs.

RELATED APPLICATIONS

This application claims the benefit of priority to U.S. ProvisionalPatent Application No. 61/826,843, entitled “System and Method forStimulating the Heart in Combination with Cardiac Rhythm ManagementPharmaceuticals” filed May 23, 2013, the entire contents of which arehereby incorporated by reference for all purposes.

BACKGROUND

The heart is divided into the right side and the left side. The rightside, comprising the right atrium and ventricle, collects and pumpsde-oxygenated blood to the lungs to pick up oxygen. The left side,comprising the left atrium and ventricle, collects and pumps oxygenatedblood to the body. Oxygen-poor blood returning from the body enters theright atrium through the vena cava. The right atrium contracts, pushingblood through the tricuspid valve and into the right ventricle. Theright ventricle contracts to pump blood through the pulmonic valve andinto the pulmonary artery, which connects to the lungs. The blood picksup oxygen in the lungs and then travels back to the heart through thepulmonary veins. The pulmonary veins empty into the left atrium, whichcontracts to push oxygenated blood into the left ventricle. The leftventricle contracts, pushing the blood through the aortic valve and intothe aorta, which connects to the rest of the body. Coronary arteriesextending from the aorta provide the heart blood.

The heart's own pacemaker is located in the atrium and is responsiblefor initiation of the heartbeat. The heartbeat begins with activation ofatrial tissue in the pacemaker region (i.e., the sinoatrial (SA) node),followed by cell-to-cell spread of excitation throughout the atrium. Theonly normal link of excitable tissue connecting the atria to theventricles is the atrioventricular (AV) node located at the boundarybetween the atria and the ventricles. Propagation takes place at a slowvelocity, but at the ventricular end the bundle of His (i.e., theelectrical conduction pathway located in the ventricular septum) and thebundle braides carry the excitation to many sites in the right and leftventricle at a relatively high velocity of 1-2 m/s. The slow conductionin the AV junction results in a delay of around 0.1 seconds betweenatrial and ventricular excitation. This timing facilitates terminalfilling of the ventricles from atrial contraction prior to ventricularcontraction. After the slowing of the AV node, the bundle of Hisseparates into two bundle branches (left and right) propagating alongeach side of the septum. The bundles ramify into Purkinje fibers thatdiverge to the inner sides of the ventricular walls. This insures thepropagation of excitatory waveforms within the ventricular conductionsystem proceeds at a relative high speed when compared to thepropagation through the AV node.

When the heart is working properly, both of its lower chambers(ventricles) pump at the same time as, and in synchronization with, thepumping of the two upper chambers (atria). Up to 40 percent of heartfailure patients, however, have disturbances in the conduction ofelectrical impulses to the ventricles (e.g., bundle branch block orintraventricular conduction delay). As a result, the left and rightventricles are activated at different times. When this happens, thewalls of the left ventricle (the chamber responsible for pumping bloodthroughout the body) do not contract simultaneously, reducing theheart's efficiency as a pump. The heart typically responds by beatingfaster and dilating. This results in a vicious cycle of furtherdilation, constriction of the vessels in the body, salt and waterretention, and further worsening of heart failure. These conductiondelays do not respond to antiarrhythmics or other drugs.

Patients who have heart failure may be candidates to receive apacemaker. A pacemaker is an artificial device to electrically assist inpacing the heart so that the heart may pump blood more effectively.Implantable electronic devices have been developed to treat bothabnormally slow heart rates (bradycardias) and excessively rapid heartrates (tachycardias). The job of the pacemaker is to maintain a safeheart rate by delivering to the pumping chambers appropriately timedelectrical impulses that replace the heart's normal rhythmic pulses. Thedevice designed to perform this life-sustaining role consists of a powersource the size of a silver dollar (containing the battery), and controlcircuits, wires or “leads” that connect the power source to the chambersof the heart. The leads are typically placed in contact with the rightatrium or the right ventricle, or both. They allow the pacemaker tosense and stimulate in various combinations, depending on where thepacing is required.

Either cathodal or anodal current may be used to stimulate themyocardium. The pulses produced by most pacemakers are typicallycathodal and excitatory. That is, the cathodal pulse is of sufficientmagnitude and length to cause the heart to beat. Cathodal currentcomprises electrical pulses of negative polarity. This type of currentdepolarizes the cell membrane by discharging the membrane capacitor, anddirectly reduces the membrane potential toward threshold level. Cathodalcurrent, by directly reducing the resting membrane potential towardthreshold has a one-half to one-third lower threshold current in latediastole than does anodal current.

Anodal current comprises electrical pulses of positive polarity. Theeffect of anodal current is to hyperpolarize the resting membrane. Onsudden termination of the anodal pulse, the membrane potential returnstowards resting level, overshoots to threshold, and a propagatedresponse occurs. The use of anodal current to stimulate the myocardiumis generally discouraged due to the higher stimulation threshold, whichleads to use of a higher current, resulting in a drain on the battery ofan implanted device and impaired longevity. Additionally, the use ofanodal current for cardiac stimulation was discouraged due to thesuspicion that the anodal contribution to depolarization can,particularly at higher voltages, contribute to arrhythmogenesis.

It has been shown that pacing in which a combination of cathodal andanodal pulses of either a stimulating or conditioning nature preservesthe improved conduction and contractility of anodal pacing whileeliminating the drawback of increased stimulation threshold. The resultis a depolarization wave of increased speed. This increased propagationspeed results in superior cardiac contraction leading to an improvementin blood flow. Improved stimulation at a lower voltage level alsoresults in reduction in power consumption and increased life forpacemaker batteries.

Over the past several years, numerous randomized clinical trials havebeen completed that show that two classes of drugs can significantlyimprove the overall survival of patients who have signs of impendingheart failure (either low left ventricular ejection fraction orincreased ventricular dilation). These two classes are β-adrenergicreceptor (beta) blockers and angiotensin-converting-enzyme (ACE)inhibitors. Beta blockers work by blocking the effect of adrenaline onthe heart, and have been noted to have numerous beneficial effects inseveral types of heart disease. Beta blockers reduce the risk of anginain patients with coronary artery disease, significantly improve thesurvival of patients with heart failure, significantly reduce the riskof sudden death in patients after heart attacks, and appear to delay orprevent the remodeling seen in the left ventricle after heart attacks.However, patients with severe asthma or other lung disease simply cannotsafely take these drugs.

ACE inhibitors block angiotensin converting enzyme, and thereby producenumerous salutary effects on the cardiovascular system. This class ofdrugs significantly improves long-term survival among survivors of acutemyocardial infarction, and in addition reduces the incidence of heartfailure (apparently by preventing or delaying remodeling), recurrentheart attacks, stroke, and sudden death.

While the use of drugs may be beneficial, following a myocardialinfarction the undamaged area of the heart is still required to workharder and the tissue damaged by the infarction remains unhealed.

SUMMARY

In an embodiment, sensors are applied to the heart and sensor data issupplied to a rules engine. The rules engine includes rules that reflectcardiac rhythm management (CRM) pharmaceuticals that have beenadministered to the patient. Using the “drug awareness” rules, the rulesengine instructs a multi-phase cardiac stimulus generator to generateelectrical waveforms that improve the performance of the drugsadministered to the patient, allow the patient to be administered alower dose of a particular drug, and/or reduce or eliminate side effectsfrom the drugs.

DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated herein and constitutepart of this specification, illustrate exemplary embodiments of theinvention, and together with the general description given above and thedetailed description given below, serve to explain the features of theinvention.

FIG. 1 is a schematic representation of the electrical activity of atypical heartbeat as is known in the prior art.

FIG. 2 is a schematic representation illustrating a cardiac stimulationdevice according to an embodiment.

DETAILED DESCRIPTION

As used herein, the term “pulse” refers to a single occurrence of anelectrical signal that has a defined shaped and period.

As used herein, the term “waveform” refers to a repeating electricalsignal that may include one or more pulses. The pulses that make up thewaveform may be the same or may differ in any one of shape, polarity,duration and amplitude. For example, a biphasic waveform may include ananodal pulse and a cathodal pulse. The anodal and cathodal componentsmay differ only in polarity or may be differ in shape, polarity,duration and amplitude. Pulses making up a waveform may differ in shape,polarity, duration, and amplitude but be equivalent in power.

As used herein, the term “sub-threshold waveform” refers to a waveformthat does not result in stimulating the heart to beat. A waveform may besub-threshold because the amplitude of the waveform is below anamplitude threshold value necessary to stimulate a heartbeat. A waveformmay be sub-threshold because the duration of the waveform is below aduration threshold value necessary to stimulate a heartbeat. A waveformmay be sub-threshold because the power of the waveform is below a powerthreshold value necessary to stimulate a heartbeat.

As used herein, the term “pacing waveform” refers to a waveform thatstimulates a heartbeat, results in depolarization and is by definitionequal to or greater than a threshold necessary to simulate a heartbeat.

FIG. 1 shows a representative tracing 10 of electrical activity in atypical heartbeat. A P wave 11 represents the wave of depolarizationthat spreads from the SA node throughout the atria. A period of timefrom the onset of the P wave to the beginning of a QRS complex is knownas the P-R interval 12. The P-R interval 12 represents the time betweenthe onset of atrial depolarization and the onset of ventriculardepolarization (typically lasting 20-200 ms). If the P-R intervalis >200 ms, there is an AV conduction block, which is also known as afirst-degree heart block if the impulse is still able to be conductedinto the ventricles.

A QRS complex 13 represents the period of ventricular depolarization,which normally occurs very rapidly (e.g., typically lasting 80-120 ms).If the QRS complex is prolonged, conduction is impaired within theventricles.

The isoelectric period (ST segment 14) following the QRS complex 13 isthe period of time (typically lasting 80-120 ms) at which the entireventricle is depolarized and roughly corresponds to the plateau phase ofthe ventricular action potential. The ST segment 14 is important in thediagnosis of ventricular ischemia or hypoxia because under thoseconditions, the ST segment 14 can become either depressed or elevated.

FIG. 2 is a schematic representation illustrating a multi-phase cardiacstimulus generator 120 implanted in a patient according to anembodiment. In an embodiment, one or more sensors sense rhythm andcontractions of the patient's heart 105 using at least one of atrialsensing and ventricular sensing, such as at least one of atrial sensor110 and ventricular sensor 112. The atrial sensor 110 and/or ventricularsensor 112 provide sensor data to a rules engine 122. In an embodiment,the rules engine includes a processor 126 and a memory 124 for storingrules and receiving sensor data. The rules engine 122 may poll the oneor more of the atrial sensor 110 and the ventricular sensor 112 toobtain sensor data and to apply the rules to the sensor data in order todetermine whether to deliver electrical waveforms to one or moreelectrodes, and, if electrical waveforms are to be delivered, which ofthe one or more electrodes is to receive the electrical waveforms. In anembodiment, the one or more electrodes may be an atrial electrode 114and a ventricular electrode 116, and may provide electrical waveforms toat least one of an atrial chamber and a ventricular chamber of the heart105. The multi-phase cardiac stimulus generator 120 may generate ananodal waveform, a cathodal waveform, and a biphasic waveform above orbelow threshold depending on the sensor data and the rules applied bythe rules engine 122.

In embodiment, if the sensor data indicate that the heart rate isnormal, and the chambers are still functioning but that the contractionsof the heart are weakening, the multi-phase cardiac stimulus generator120 generates a sub-threshold biphasic waveform. The sub-thresholdbiphasic waveform may be applied to either the atria or the ventricles.For example, the sub-threshold biphasic waveform may be applied to theatrial electrode 114 or to ventricular electrode 116. In an embodiment,a PR-interval is sensed using atrial sensor 110 indicating that theatrium has contracted. The sub-threshold biphasic waveform may beapplied during this interval.

In an embodiment, following the administration of the sub-thresholdbiphasic waveform, the rules engine 122 updates the sensor data anddetermines whether the cardiac contractions have improved. If thecontractions have improved, application of sub-threshold biphasicwaveforms is suspended. The rules engine 122 continues to monitor thesensor data from atrial sensor 110 to determine whether to resume theapplication of sub-threshold biphasic waveforms to the heart 105.

In an embodiment, following the administration of the sub-thresholdbiphasic waveform, the rules engine 122 used the sensor data todetermine whether either the atrium or ventricles have depolarized. Ifdepolarization is sensed, the biphasic waveform can be stopped.

The application of a sub-threshold biphasic waveform to either theventricles or to atrium results in improved function (contraction) ofthe chamber to which it is applied.

In an embodiment, when weak atrial contractions lead to inadequatefilling of the ventricles and poor loading of the left ventricle priorto systole, application of a sub-threshold biphasic waveform to theatria results in an increased amount of blood being supplied to theventricle and aiding both chambers. In an embodiment, when it is sensedthat application of the sub-threshold biphasic waveform alone is notproviding adequate treatment, a biphasic waveform can additionally begiven to the ventricle as well.

In an embodiment, in a cycle in which the atrium or ventricles do notdepolarize on their own, the sub-threshold biphasic waveform is stoppedafter a reasonable time, generally on the order of the QT interval,which is approximately 400 milliseconds. For the next heartbeat, theamplitude of the cathodal part of the sub-threshold biphasic waveformcan be increased, and this can occur repeatedly until a contraction doesoccur.

In an embodiment, the rules engine 122 can determine from the sensordata received from the atrial sensor 110 whether to apply asub-threshold biphasic waveform or a stimulatory biphasic waveform tothe atrial electrode 114.

In another embodiment, a sub-threshold biphasic waveform may beadministered to the atrial electrode 114 when the sensor data from theatrial sensor 110 indicate the presence of atrial fibrillation.Following application of the sub-threshold biphasic waveform to theatrial electrode 114, the rules engine 122 may monitor the one or moreventricular sensor 112 to determine whether the ventricle contracts(ventricular beat) in response to the sub-threshold biphasic waveformapplied to the atrial electrode 114. In an embodiment, the ventricularbeat is determined by the presence of a QRS waveform.

In another embodiment, the rules engine 122 determines whether followingthe application of the sub-threshold biphasic waveform to the atrialelectrode 114 the heart 105 produces a QRS waveform (See, FIG. 1). Whena QRS waveform is detected, the application of the sub-thresholdbiphasic waveform is suspended. When a QRS waveform is not detectedafter application of the sub-threshold biphasic waveform, the rulesengine 122 causes the multi-phase cardiac stimulus generator 120 togenerate a cathodal pacing waveform for delivery to ventricularelectrode 116. In an embodiment, the amplitude and/or the length of thecathodal waveform may be lower following the application of asub-threshold anodal waveform to the atrial electrode 114.

In an embodiment, sensors are applied to the heart and sensor data issupplied to a rules engine. The rules engine applies rules that reflecta CRM pharmaceutical regime of the patient. Using the drug “awareness”rules, the rules engine instructs a multi-phase cardiac stimulusgenerator 120 to generate electrical waveforms that improve theperformance of the drugs administered to the patient, that allow thepatient to be administered a lower dose of a particular drug, and/orthat reduce or eliminate side effects from the drugs.

In an embodiment, a biphasic pacing waveform is used in conjunction withadministration of a CRM pharmaceutical, such as, for example, digitalis,nor epinephrine, epinephrine, phosphodiesterase inhibitors, and calciumsensitizing drugs. The biphasic waveform is generated using the drug“awareness” rules described above.

The combination of biphasic pacing with a pharmaceutical can lead to alower dosage of the pharmaceutical during what would normally be theloading dose phase. By using biphasic pacing in conjunction with a lowerloading dose, toxic levels of the loading dose may be avoided. A safemaintenance dose may thus be given over a longer period of time whenused in conjunction with biphasic pacing.

Digitalis, for example, increases contraction of the heart. However, theincrease in contraction comes with the risk of toxic side effects. Whenused alone, digitalis is initially given at a “loading dose” ofapproximately 0.25 mg four times per day for three days. Subsequently, amaintenance dose of 0.25 mg is administered. The combination of biphasicpacing with digitalis can lead to lower dosage of the drug during themore dangerous loading dose phase.

The combination of biphasic pacing with a pharmaceutical can also leadto lower stimulation voltage for pacing and improve battery life.Because of the lower pacing voltage, there is less damage to heart thattypically accompanies pacing.

Certain drugs, such as beta blockers, quinidine, and otheranti-arrhythmia drugs such as those given to atrial fibrillationpatients are known to reduce contractility. Biphasic pacing offers theopportunity to uses a lower dosage of those drugs to avoid unwanted sideeffects.

A system and method for stimulating the heart in combination with CRMpharmaceuticals in an artificially paced heart have been disclosed. Itwill also be understood that the invention may be embodied in otherspecific forms without departing from the scope of the inventiondisclosed and that the examples and embodiments described herein are inall respects illustrative and not restrictive. Those skilled in the artof the present invention will recognize that other embodiments using theconcepts described herein are also possible. Further, any reference toclaim elements in the singular, for example, using the articles “a,”“an,” or “the” is not to be construed as limiting the element to thesingular.

What is claimed is:
 1. An apparatus configured to deliver electricalwaveforms to a patient's heart comprising: a multi-phase cardiacelectrical waveform generator; one or more sensors configured to sense acondition of a human heart; one or more electrodes configured to beimplanted on, in, or proximate to at least one of an atrial chamber anda ventricular chamber of the heart; a memory configured to store rulesthat account for a pharmaceutical regime of the patient; and a processorconfigured to: poll the one or more sensors to obtain sensor data; applythe rules from the memory to the sensor data to determine whether thesensor data indicates weakening contractions of the patient's heart;determine whether to deliver a sub-threshold electrical waveform that isinsufficient to cause the heart to beat to at least one of the one ormore electrodes to improve the contractions of the patient's heart;instruct the multi-phase cardiac electrical waveform generator togenerate the sub-threshold electrical waveform when it is determined todeliver the sub-threshold electrical waveform to at least one of the oneor more electrodes; and deliver the sub-threshold electrical waveform ata timing determined from the sensor data; poll the one or more sensorsto obtain updated sensor data after delivery of the sub-thresholdelectrical waveform; and determine whether to suspend delivery of thesub-threshold electrical waveform based on presence of a QRS waveform inthe updated sensor data.
 2. The apparatus of claim 1, wherein theprocessor is further configured to determine whether to deliver a pacingelectrical waveform by applying the rules from the memory to the sensordata, instruct the multi-phase cardiac electrical waveform generator togenerate the pacing electrical waveform when it is determined to deliverthe pacing electrical waveform to at least one of the one or moreelectrodes, and deliver the pacing electrical waveform at a timingdetermined from the sensor data.
 3. The apparatus of claim 2, whereinthe pacing waveform is a biphasic waveform.
 4. The apparatus of claim 1,wherein the processor suspends delivery of the sub-threshold electricalwaveform when the updated sensor data indicates that the human heart hasgenerated the QRS waveform.
 5. The apparatus of claim 1, wherein theprocessor continues delivery of the sub-threshold electrical waveformwhen the updated sensor data indicates that the human heart has notgenerated the QRS waveform.